This invention relates to a method of treating waste water. The invention has particular application to the treatment of waste water where there is a relatively long period before the waste water is discharged. This invention has particular but not exclusive application to the treatment of sewerage effluent and for illustrative purposes only reference will be made to this application.
The conventional method of treating sewerage involves firstly collecting sewerage effluent through a conduit system of sewerage conduits and delivering it to a sewerage treatment plant at or close to the site where the treated effluent will be released. At the conventional sewerage treatment plants, the sewerage effluent undergoes a series of anaerobic and aerobic incubations to remove waste including organic matter, other solids, nitrogen and phosphate and disinfection to reduce the number of pathogenic organisms in the sewerage effluent prior to its release.
As the sewerage effluent passes through the sewerage mains and pumping stations, the sewerage effluent becomes an incubating culture. The composition of the sewerage effluent is continuously changing during its passage. Many of the reactions promoted by the naturally occurring micro-organism populations are undesirable. And produce reaction products such as hydrogen sulphide and ammonia and possibly also other nitrogenous containing compounds such as mercaptans. For example they cause major odour problems in the areas near pumping wells and also produce nasty gaseous chemicals that tend to corrode the conduits and other surfaces in the conduit system.
Further when the sewerage reaches the sewerage plant it has deteriorated in the sense that it contains more complex chemicals and is more difficult to treat than when it entered the system. These chemicals have been generated by the reactions propagated by the naturally occurring micro-organism populations in the conduit system. As a consequence the treatment of the sewerage at the treatment plant involves more unit operations and is more technically difficult than would otherwise be the case.
For example a common problem is the proliferation of filamentous bacteria incubating in a nutrient rich environment. The foaming problem in aerobic tanks results in the need for additional treatment and extends the time for treatment before the treated sewerage effluent can be released. These problems cause the cost of treatment to rise.
In the specification the term xe2x80x9ccomprisingxe2x80x9d shall be understood to have a broad meaning similar to the term xe2x80x9cincludingxe2x80x9d and will be understood to imply the inclusion of a stated integer or step or group of integers or steps but not the exclusion of any other integer or step of group of integers or steps. This definition also applies to variations on the term xe2x80x9ccomprisingxe2x80x9d such as xe2x80x9ccomprisexe2x80x9d and xe2x80x9ccomprisesxe2x80x9d.
According to one aspect of this invention there is provided a method of treating waste water passed through a conduit system comprising at least one conduit extending from at least one entry point to a discharge point and including at least one quiescent zone where water is at least temporarily slowed in its displacement towards the discharge point, the method including introducing an inoculum into the system at at least one primary inoculation site for facilitating its entry into the quiescent zone where it incubates and forms an inoculum culture that influences the type and quantity of certain micro-organism populations in the system both within the quiescent zone and downstream thereof, the inoculum culture encouraging micro-organisms that assist with the break down or degradation of organic compounds within the waste water and retarding micro-organisms that tend to form undesirable compounds from the organic compounds in the waste water
Applicant has noted that sustained high velocity water flow significantly retards production of negative effects in waste water streams. Conversely, applicant has noted that unfavourable organisms tend to flourish in these quiescent zones where they attach to the surfaces of the conduit and the like. The organisms attach to both submerged surfaces in contact with the water and exposed surfaces in contact with the gas or air space above the surface of the water. This incubation of cultures of the harmful micro-organisms in the quiescent zones occurs because of the fact that the water does not have a significant path length or longitudinal velocity in these zones. The cultures produce chemical compounds that release toxic gases, eg hydrogen sulphide, and compounds that attack the materials of the conduit, eg concrete.
Applicant has discovered that these same quiescent zones can be used to produce positive reactions in the waste water (i.e. partial break-down) by a careful process of introduction of beneficial organisms (i.e. those which work to effect break-down of organic matter in the waste stream without large scale production of negative substances or effects) to the system by incubating an inoculum. This allows organisms which would not otherwise flourish (or would otherwise be out-competed) to maintain viable populations. Put another way the micro-organism population can be altered to produce catabolic-type reaction products rather than more complex anabolic reaction products.
Thus an inoculum is introduced to a quiescent zone where it encourages the propagation of beneficial organisms and suppresses the growth of harmful organisms, ie that react with the waste compounds to produce undesirable compounds such as ammonia and hydrogen sulphide.
In this specification the term quiescent zone means a zone somewhere along the length of the pipe where the water flow is interrupted or at least significantly reduced. The typical flow through the conduit resembles plug flow where all water is travelling at the same speed through the conduit towards the discharge point. However in the quiescent zone the water does not significantly advance towards the discharge point although there may be internal mixing in the zone. A quiescent zone may for example be formed by a pumping well, a low point at the interconnection of two conduit sections or any other zone where part of the pipe is exposed and water vapour collects. A quiescent zone may also occur intermittently in a given conduit in relation to intermittent cycles of a pump or variations in volumes of flow through the conduit.
The culture incubated by the inoculum typically comprises both aerobic and anaerobic micro-organisms and the micro-organisms in the inoculum culture typically exist in a symbiotic relationship with each other. Thus when the micro-organisms in the inoculum culture are carried by the water into an anaerobic environment a viable population of aerobic organisms will remain and when the micro-organisms incubated by the inoculum culture are carried in the water into an aerobic environment a viable population of anaerobic micro-organisms will remain.
Applicant has noted that the cultures of undesirable micro-organisms which produce negative effects in waste water systems (e.g. odour, aggressive atmospheres) are largely located on the surfaces of the conduits in the quiescent zones as distinct from in the waste water itself. Accordingly it is the cultures on the surfaces of the quiescent zones which have to be addressed. Prior methods have assumed that cultures causing negative effects are resident primarily in the water as distinct from on the surfaces which is incorrect.
Typically the system includes at least one surface, typically a plurality of surfaces, in the quiescent zone and the miro-organisms formed by the inoculum adhere tenaciously to the surface/s of the system.
The surfaces may be formed by the conduits and the micro-organisms formed by the inoculum preferably have the ability to adhere at least as tenaciously to the surface/s as the harmful microorganisms in the system.
The introduction and nurturing of these beneficial organisms at specific sites and the resultant positive effects (and suppression of negative effects) is the basis of this invention.
The inoculum culture may be introduced into the quiescent zone either directly or indirectly. By indirect introduction is meant putting the culture into the conduit/s either upstream or downstream of the quiescent zone and letting the fluid flow in the system, ie gas or liquid, carry it to the zone. More specifically the inoculum culture may be introduced indirectly into the quiescent zone by being introduced into the water upstream of the quiescent zone and allowing it to flow with the water to the quiescent zone. Alternatively the inoculum culture may be introduced into an air space in the conduit as fine droplets either upstream or downstream of the quiescent zone, and be carried by the air upstream to the quiescent zone.
The inoculum may include photosynthetic micro-organisms, heterotrophic bacteria, and lactic acid bacteria and the inoculum may further include a substrate.
The inoculum of selected microorganisms is preferably a mixed population the proportions of which may vary depending on the type of waste introduced into the waste water reticulation system. Further, the type of microorganisms selected may vary depending on the type of waste introduced into the waste water reticulation system. For example, where the waste introduced into the waste water reticulation system has a high proportion of fat or oil, lactic acid bacteria may be selected and an inoculum may contain a high proportion of lactic acid bacteria compared with other microorganisms. In creating the conditions where an inoculum contains a high proportion of lactic acid bacteria a relatively large amount of sugar may be added during preparation of the inoculum to serve as a substrate for lacto-bacillus and other fermentative organisms which as a consequence forms a combination of lactic and acetic acids that assists in degrading the fat and oil substrates. The selected microorganisms are chosen because of their ability to co-operate in reducing the waste to small molecular weight products, including water and CO2. The microorganisms are preferably chosen based on their ability to breakdown each other""s products.
The inoculum may include purple non-sulphur producing heterotrophic photosynthetic bacteria, lactobacillus, yeasts, actinomycetes, Nocardia species, ray fungi, plankton and other chemoautotrophic bacteria. In a preferred form the inoculum is produced from the EM (Effective Microorganisms) formulation which is commercially available.
Often the conduit system has a plurality of conduits and specifically a plurality of conduits in parallel. The method may include introducing inoculum into a plurality of primary inoculation sites located in parallel conduits.
This enables a widespread conduit network, with many branches towards the upstream end thereof, to be treated in a way that has an effect throughout the system. The inoculum is introduced to a quiescent zone in each of the conduits.
Preferably each primary inoculation site is positioned such that at least 50% of the water passing through the primary inoculation site has spent less than 25% of its total residence time in the system when it passes through the inoculation site.
Very often the conduit systems are long and contain a plurality of quiescent zones along their length and it is desirable to introduce further inoculum downstream of the primary inoculation site. This replenishes the culture of beneficial micro-organisms and perpetuates or maintains the favourable environment produced by the inoculum further downstream in the conduit system.
The conduit systems may include at least one secondary inoculation site positioned downstream of the primary inoculation site/s, each secondary inoculation site introducing inoculum to a yet further quiescent zone and positioned such that at least 50% of the water passing through the site has spent 50 to 75% of its residence time in the system.
Preferably the system also includes at least one further inoculation site called a tertiary inoculation site downstream of the secondary inoculation site. The purpose of the tertiary inoculation site is the same as the secondary inoculation site namely to bolster and maintain the culture of beneficial micro organisms at an appropriate level in a downstream quiescent zone through which the water passes before it reaches the discharge point.
Typically there is only one tertiary inoculation site and substantially all of the water flows through the site. Preferably the tertiary site is positioned such that the water passing therethrough has spent 50 to 80% of its residence time in the conduit system. Further preferably the tertiary inoculation site is positioned so that the inoculum introduced at the site is incubated in a quiescent zone, eg a pumping well prior to the rising main or a quiescent zone in the rising main. A tertiary site inoculation is preferred where more than 750 kiloliters per day of effluent or waste is collected for transfer by rising main of more than one thousand meters in length.
The secondary and tertiary inoculation sites serve to boost the population of the selected microorganisms. As indicated above, the waste water effluent in a waste water reticulation system is dynamic and undergoes constant change depending on the conditions that prevail at different stages in the waste water reticulation system. As a result of incubation at any one particular zone, the population of some of the selected microorganisms will increase whereas the population of other selected microorganisms will decrease. It is therefore preferred that the waste water effluent is subjected to further inoculation as it travels through the waste water reticulation system. By inoculating the waste water effluent again the population of the desired selected microorganisms can be increased and thus continue to degrade the waste in the waste water effluent. The subsequent inoculation can effectively augment deficiencies in the culture of the previously inoculated waste water effluent. In this way, a blanket effect is achieved which covers substantially all of the incubating cultures affecting the waste water effluent and found in quiescent zones throughout the system.
Generally the amount of inoculum introduced into the conduit system per unit time may be a function of the surface area of the interior surface of the conduit system and the volume or size and number of quiescent zones through which the effluent passes and not necessarily related to the volume of water flowing through the system.
The difference between dosage rates of inoculum at the various primary inoculation sites may be less than 20%, preferably less than 5%. More preferably the dosage rates are substantially the same across a majority of the sites. However often a system will have one or more sites having higher dosage rates. This is due to the fact that the positioning of the sites has to fit in with the existing characteristics of the conduit system. Usually the sites having higher dosage rates are secondary and tertiary sites although they may also include primary sites.
The method may further include providing at least two secondary inoculation sites positioned downstream of the primary inoculation site/s, and having the difference between dosage rates of inoculum at the secondary inoculation sites being less than 20%, preferably less than 5%. More preferably the dosage rates are substantially the same across all the secondary sites.
Where the conduit has at least one tertiary site, the difference between dosage rate of inoculum between the tertiary site and the secondary sites may be less than 20%.
Each of the primary and secondary inoculation sites may have a difference in dosage rate of not more than 5%.
In this invention the conduit system is used to effectively treat the sewerage effluent before it reaches the discharge point. The invention uses rising mains, gravity mains and various pumping wells as quiescent zones to incubate specific cultures of microorganisms. The inoculation with selected microorganisms results in competition for available nutrients and thus alters the type and number of microorganisms and the type and quantity of fermentation products produced in the sewerage effluent.
According to another aspect of this invention there is provided a method of treating waste water passed through a conduit system comprising at least one conduit extending from at least one entry point to a discharge point the method including introducing an inoculum into the system at at least two inoculation sites longitudinally spaced apart from each other along the conduit system, the sites being used to introduce inoculum to the conduit system where it incubates and forms an inoculum culture that influences the type and quantity of certain microorganism populations in the system both proximate to the inoculation site and downstream thereof, the inoculum culture encouraging micro-organisms that assist with the break down or degradation of organic compounds within the system and retarding micro-organisms that tend to form undesirable compounds from the organic compounds in the system.
Advantageously the location of the spaced sites is chosen such that the negative substrates produced by normally occurring populations of micro-organisms incubated within the conduit system are relatively stable downstream of the site and the substrates produced by populations of the micro-organisms established at a said site would not vary dramatically, that is by more than 20% between the inoculation site and a point downstream of the site. This point may be proximate or it may be remote. This indicates a resistance to uncontrolled swings in populations of undesirable micro-organisms (blooms). This stability is very important to any program aimed at treating the water.
The spacing of the inoculation sites may be chosen such that the substrates produced by populations of micro-organisms fostered by the inoculum culture are relatively stable and would not vary by more than 20% at any points along the conduit path between longitudinally spaced inoculation sites. The downstream sites are chosen to suitably boost the population of favourable microorganisms at the appropriate point along the conduit system and are positioned so as to do this before any major changes in substrates and populations occur.
Preferably the dosage rate of inoculum at each of the inoculation sites is substantially the same and the inoculum is delivered regularly and evenly over a unit time period.
The system may have either two or three said inoculation sites longitudinally spaced apart from each other, preferably three.
Inoculation at an inoculation site preferably occurs by inoculation means which may include spraying of inoculum from a nozzle or passing waste water over a support medium seeded with selected microorganisms. Inoculation sites may be associated with sewerage mains, pump wells, silt collection traps and transfer stations. In addition, the surface area in the collection and transfer network provides potential sites for support mediums of inoculating microorganisms.
The inoculation means may include an inoculation chamber which is positioned between two mains and serves as a site to inoculate waste water effluent. The inoculation chamber may be positioned in a pump well or inline between conduits.
The inoculation means employed at a particular site will depend on the conditions at the site. For example, where the level of anaerobic activity will be high because of long rising mains or long retention time due to slow flow, aerosol inoculation is preferred as it allows proliferation of augmented aerobic and heterotrophic organisms to help maintain a balance of aerobic and anaerobic activity and this is particularly relevant where the inoculum contains organisms which allow an increased level of dissolved oxygen to appear in the effluent during anaerobic activity. In another example where there are long gravity mains and there will be relatively high aerobic activity, a support medium of seeded selected microorganisms are positioned so that effluent passing over is inoculated with the microorganisms. This allows proliferation of augmented anaerobic organisms in the effluent to help maintain a balance of aerobic and anaerobic activity allowing some increased anaerobic activity in a largely aerobic environment.
The inoculum of selected microorganisms may be prepared by a batch process or alternatively a continuous process.
The incubated inoculated effluent in the inoculation chambers allows the selected microorganisms to adapt to and reproduce in the effluent and in the quiescent zones associated with the effluent as a partially prepared medium source. This reduces the environmental shock load on the selected microorganisms when they are released to the reticulation system. In a pump well inoculation chamber the subsequent culture may incubate until a sensor signals for the release of the culture into the mains. In an in-line inoculation chamber the subsequent culture constantly incubates in the system and the flow of water releases the culture. The incubating culture in the inoculating chamber serves to inoculate further untreated effluent.
The inoculation means may include an inoculum reservoir having a housing, an inoculum source contained within the housing and means for dispensing the inoculum at a particular site. The inoculum may be in a concentrated form and be diluted prior to being dispensed. Other additives may be dispensed with the inoculum. Other additives may include acetic acid, citric acid, or sugar solutions.
In another aspect, the invention broadly resides in an inoculation chamber including
a housing with a waste water inlet and a waste water outlet; and
a support medium means seeded with selected micro-organisms wherein the waste water substantially passes over and through the support medium and is inoculated with micro-organisms released therefrom.
The support medium means preferably includes a base layer of sand or crushed rock such as crushed blue metal but preferably zeolite. The support medium preferably includes a second layer of porous clay or concrete bricks. Alternatively the second layer may include crushed rock such as blue metal that has a larger diameter than the material used for the first layer. The support medium means preferably includes a third layer of similar material as used in the first layer such as zeolite. The support medium means preferably includes a fourth upper layer of biologically activated ceramic. The biologically activated ceramic preferably includes selected microorganisms contained therein. The biologically activated ceramic preferably is arranged so that the waste water effluent becomes mixed, aerated with turbulence and inoculated with microorganisms therefrom.
The inoculation chamber may also include a spray means for providing a spray inoculum to the waste water flowing into the chamber and to surfaces of the inoculation chamber, including the support medium.